1. Significant amounts of pure sprinting/heavy lifting/plyo
2. anaerobic intervals aimed at lactate threshold
3. Some form of aerobic work such as Clyde Hart's "slow 200m intervals" building up to faster ones over the season.

Speed/strength/plyo obviously is paramount, and most people use intervals.... but considering that 400/800 is basically a hybrid of sprint/endurance and there is a significant "aerobic" component there must be some sort of aerobic work stashed in there (and anaerobic intervals do not necessarily count as such).

I haven't really kept up with current 400/800m runners in a bit, but it seems like most of them are lacking the speed reverse (aka they need to work on getting faster).

Bolt is obviously coming from the opposite perspective, so he needs to build up lac threshold and aerobic base some then he will dominant because he has such as huge speed reserve.

That's my take at least... I dunno maybe you have a different approach?

Close enough in agreement (which is why I asked you to go beyond the studies and actually give something concrete...discussing studies is pretty well useless), though I think much of the aerobic can be gained from stressing the anaerobic with short rest periods, like in intensive/extensive tempo. Higher volume, lower intensity in early season, decreasing volume & increasing intensity as the season progresses.

Notice one thing with Clyde Hart's slow 200m intervals...as the season progresses, they become intensive/extensive tempo for anyone, 5 x 200m in 25 is significant percentage of most people's max...for even a 20 second 200m runner, that's 80% of max - the intensive tempo range, i.e., anaerobic intervals. 6x26, 7x27, even 8x28...those are in the extensive tempo range for even the superstars. He does more overdistance work than others, but there are many roads to Rome.

As I said before, the slower aerobic work is predominantly to build a base from which to work in the season on the faster stuff, the bread and butter, the actual speed-endurance component. The aerobic work, as far as I can tell, is not aimed specifically at building a better 400m runner, but at building a better athlete...it's long sprinter GPP, essentially.

"Speed reserve" is all well and good, but keep in mind, there is a reason why 100m sprinters don't dominate the 400m. And it's not a lack of speed reserve (no matter how many times you use the phrase )...Gay, Powell, Dix, and Bolt will all have about the same speed reserve since they're all in the same level of the stratosphere. So why aren't they out there killing the 400m? I doubt it's because they're nice guys that want to let Wariner (who is no 200m slouch at 20.19 and having plenty of "speed reserve" himself) and Merritt (a touch faster in the 200m, a touch slower in the 400m vs. Wariner's PRs) have a shot at something.

Maybe it's a lack of desire to endure the pain of 400m training or maybe it's that the best short sprinters don't make the best long sprinters or maybe it's that they'd have to give up short track dominance to dominate in long sprints....or maybe it's some other combination of possibilities.